Assessment Comments

Assessment is based on results of IDNR beach monitoring during 2000 and 2001. See attached document for details.

Basis for Assessment

Not assessed for previous Section 305(b) reports.

SUMMARY:  The Class A (primary contact recreation) uses were assessed as "not supported."  The source of data for this assessment is the IDNR beach monitoring program in 2000 and 2001.   The Class B(WW) aquatic life uses and fish consumption uses were not assessed due to lack of water quality information.   EXPLANATION:  According to U.S.  EPA guidelines, primary contact recreation uses are "not supported" if the geometric mean of fecal coliform bacteria levels exceeds 200 orgs/100ml based on at least five samples in a 30-day period (see U.S.  EPA 1997b, page 3-35).   The Iowa water quality criterion to protect primary contact recreation uses is 200 organisms/100 ml.   During the recreational season of 2000, seven of eight 30-day periods had geometric means (N=5) greater than 200 organisms/100 ml; the maximum 30-day geometric mean was 2,291 organisms per 100 ml.   During the recreational season of 2001, four of 13 30-day periods had geometric means greater than 200 organisms; the maximum 30-day geometric mean was 638 organisms/100 ml.   Thus, based on geometric mean value greater than 200 organisms per 100 ml, the primary contact recreation uses were assessed as "not supported."  Also, according to U.S.  EPA guidelines, beach closures of more than one week's duration per year suggests nonsupport of the primary contact recreation uses (see U.S.  EPA 1997b, page 3-34).   Backbone beach was closed for 10 weeks during 2000 and for 5 weeks in 2001.   Thus, these beach closures also suggest nonsupport of the primary contact recreation uses.